Dielectric resonator structure having resonator displaceable between support plates for adjusting resonance frequency

ABSTRACT

A dielectric resonator structure includes a resonator made of a dielectric material. The resonator is supported between two support plates and can be displaced at least in one direction between the plates. At least one of the plates is made of a dielectric material so that the amount of the dielectric material of the support plate varies in the direction of displacement of the resonator.

FIELD OF THE INVENTION

The invention relates to a dielectric resonator structure comprising aresonator made of a dielectric material.

BACKGROUND OF THE INVENTION

Among high-frequency and microwave resonator structures, so-calleddielectric resonators have recently become increasingly interesting asthey offer e.g. the following advantages over conventional resonatorstructures: smaller circuit sizes, higher integration level, higherefficiency and lower cost of manufacture. Any element having a simplegeometric shape and being made of a material of low dielectric lossesand a high relative dielectric constant can be used as a high-Qdielectric resonator. For reasons of the manufacturing technique thedielectric resonator is usually cylindrical, such as a cylindrical disc.

The structure and operation of dielectric resonators are described e.g.in the following articles:

[1] Ceramic Resonators for Highly Stable Oscillators, Gundolf Kuchler,Siemens Components XXIV (1989) No. 5, p. 180-183.

[2] Microwave Dielectric Resonators, S. Jerry Fiedziuszko, MicrowaveJournal, September 1986, p. 189-191.

[3] Cylindrical Dielectric Resonators and their Applications in TEM LineMicrowave Circuits, Marian W. Pospieszalski, IEEE Transactions onMicrowave Theory and Techniques, VOL. MTT-27, No. 3, March 1979, p.233-238.

The resonance frequency of the dielectric resonator is primarilydetermined by the dimensions of the resonator element. Another factoraffecting the resonance frequency is the surroundings of the resonator.The electric or magnetic field of the resonator and thus the resonancefrequency can be intentionally affected by introducing a metal surfaceor any other conductive surface in the vicinity of the resonator. Toadjust the resonance frequency of the dielectric resonator, a commonpractice is to adjust the distance between the conductive metal surfaceand the planar surface of the resonator. The adjusting mechanism may bee.g. an adjustment screw attached to the housing surrounding theresonator.

In this kind of adjusting method, however, it is typical that theresonance frequency varies non-linearly as a function of the adjustingdistance. Due to the non-linearity and the steepness of the adjustment,it is difficult and requires high precision to accurately adjust theresonance frequency, especially in the upper end of the adjusting range.In addition, the unloaded Q-factor varies as a function of the distancebetween the conductive surface and the resonator.

A constant Q-factor and more linear frequency adjustment can be obtainedwithin a wider range by replacing the conductive adjustment surface orplate with a dielectric adjustment plate the distance of which from theplanar surface of the resonator is adjusted. FIG. 7 in theabove-mentioned article [2] shows a so-called double resonator structureas a modification of this solution. In the double resonator structure,two cylindrical dielectric resonator discs are positioned co-axiallyclose to each other so that the distance between their planar surfacescan be adjusted by displacing the discs in the direction of their commonaxis. Also in this case the adjustment curve is still steep, in additionto which the double resonator structure is larger and more complicatedthan a conventional structure utilizing an adjustment plate.

SUMMARY 0F THE INVENTION

The object of the invention is to provide a dielectric resonatorstructure in which the resonance frequency can be adjusted moreaccurately than was previously possible.

This is achieved by means of the dielectric resonator structureaccording to the invention, wherein the resonator is supported betweentwo support plates and displaceable at least in one direction betweenthe support plates, at least one of the support plates being made of adielectric material so that the amount of the dielectric material of thedielectric support plate varies in a direction of displacement of theresonator.

The basic idea of the invention is that the resonance frequency isadjusted by varying the amount of dielectric material in the vicinity ofthe resonator by moving the resonator in place of the frequencyadjuster. In the preferred embodiment of the invention, the resonatordisc is attached and supported by means of dielectric support plates atleast one of which comprises an opening of a predetermined shape. Theadjustment of the resonance frequency of the resonance circuit takesplace by moving the resonator with respect to the form openings of thesupport plates, so that the amount of the ceramic material adjusting theresonance frequency varies in the vicinity of the resonator as afunction of the adjusting movement. The invention provides a simpler andmore compact structure, since the separate frequency adjustment andsupport structures are omitted. As all the structures can be made of adielectric material, temperature compensation will be facilitated andthe Q-factor of the resonator remains constant during the frequencyadjustment. By suitably selecting the size/shape of the form openings, aresonance frequency adjustment curve having a desired slope andlinearity is achieved. The gently sloping, linear adjustment curve, inturn, results in better accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail bymeans of illustrating embodiments with reference to the attacheddrawings, in which:

FIG. 1A shows a cross-sectional side view of a resonator structureaccording to the invention;

FIGS. 1B and 1C show sections taken along the lines 1--1B and 1C--1C,respectively, of the resonator structure of FIG. 1A;

FIG. 2A shows the resonator structure of FIG. 1A when the resonator hasbeen displaced; and

FIG. 2B shows a section taken along the line 2B--2B of the resonatorstructure of FIG. 2A.

DETAILED DESCRIPTION

As used herein, the term dielectric resonator refers generally to anybody or element of a suitable geometric shape and made of a material oflow dielectric losses and having a high relative dielectric constant.For reasons of manufacturing technique, the dielectric resonator isusually cylindrical, such as a cylindrical disc. The most commonly usedmaterial is ceramic.

The structure, operation and ceramic materials of dielectric resonatorsare described e.g. in the above-mentioned articles [1], [2] and [3],which are incorporated in the present application for reference. In thetext below the structure of the dielectric resonator will be describedonly to such an extent as is necessary for the understanding of theinvention.

The figures show a cross-section of a dielectric resonator structure 1according to the preferred embodiment of the invention, comprising adielectric, cylindrical resonator element 3 positioned in a cavity 5defined by a housing 2 made of an electrically conductive material (suchas metal). The housing 2 is connected to ground potential. Thedielectric resonator element 3, typically made of a ceramic material, issupported between two parallel support plates 4A and 4B at a fixeddistance from the bottom and cover of the housing 2. The lower surfaceof the upper support plate 4A is pressed against the upper radial planarsurface of the cylindrical resonator disc 3 while the upper surface ofthe lower support plate 4B is correspondingly pressed against the lowerplanar surface of the resonator disc 3, so that the resonator disc 3 isradially displaceable between the support plates 4A and 4B. The lowerand upper surfaces of the support plates 4A and 4B are preferablyprovided with recesses or grooves 7 having a width equal to the diameterof the resonator disc 3. The resonator disc 3 is positioned in therecesses or grooves, which determine the direction of movement of thedisc 3, indicated by the arrow 9.

The electromagnetic fields of the dielectric resonator extend outsidethe resonator element, and so the resonator can be electromagneticallyconnected to another resonator circuit in various ways, depending on theapplication, such as by a microstrip conductor, a bent coaxialconductor, or a conventional straight conductor positioned close to thedielectric resonator. In the example of FIG. 2A, the connection to theresonator 3 is made by means of a bent inner conductor 6A of a coaxialcable 6.

The resonance frequency of the dielectric resonator is determined mainlyby the dimensions of the resonator element. Another factor affecting theresonance frequency is the surroundings of the resonator. By introducinga metal surface or some other conductive surface in the vicinity of theresonator, the electric or magnetic field of the resonator and thus alsothe resonance frequency can be intentionally affected. A similar effectis produced when a dielectric body is brought close to the resonatorexcept that the unloaded Q-factor of the resonator does not vary in thiscase.

In the resonator structure 1 according to the invention, at least one ofthe support plates 4A and 4B is made of a suitable dielectric materialso that it affects the resonance frequency of the resonator 3. Thesupport plate 4A is provided with a form opening 8 the shape and size ofwhich vary in the direction of displacement of the resonator disc 3. Theform opening 8 also causes the amount of the dielectric material in theimmediate vicinity of the resonator disc 3 to vary in the direction ofdisplacement of the resonator disc 3, which, in turn, varies theresonance frequency. By suitably selecting the size and shape of theform opening 8, a desired interdependence can be achieved between thelinear movement (location in the direction of movement) of the resonatordisc 3 and the resonance frequency. FIGS. 2A-2B show the resonatorstructure when the resonator disc has been displaced in the directionindicated by the arrow 9 to the left from the position shown in FIGS.1A-1C.

Alternatively, the support plates 4A and 4B can both be ceramic and bothof them may comprise form openings 8. From the point of view oftemperature compensation, it is preferable that the support plates 4Aand 4B are both dielectric.

The adjusting mechanism may, for instance, comprise an adjusting screwor rod 9 attached to the edge of the resonator disc 3 by means of aninsulator spacer 9A, as shown in FIG. 2A.

The invention has been described above by way of example by means of aspecific embodiment. As is obvious to one skilled in the art on thebasis of the above, the adjusting principle according to the inventioncan, however, be applied in all dielectric resonator structures in placeof conventional adjusting methods. A few examples of possible structuresare given in the above-mentioned articles [1]-[3].

The figures and the description related to them are only intended toillustrate the present invention. In its details the resonator structureaccording to the invention may vary within the spirit and scope of theattached claims.

I claim:
 1. A dielectric resonator structure, comprising:a resonatormade of a dielectric material; a pair of two spaced apart butconfronting support plates, said resonator being supported between saidplates; means for displacing said resonator between said support plates,in at least one direction that is parallel to said support plates; atleast one of said support plates being made of a dielectric material andhaving an opening provided therethrough, the width of said openingcrosswise of said direction varying in said direction if relative tosaid resonator as a result of said resonator being displaced in saiddirection by said means for displacing.
 2. The resonator structure ofclaim 1, wherein:both of said support plates are made of a dielectricmaterial.
 3. The resonator structure of claim 2, wherein:both of saidsupport plates have a respective said opening, the width of each saidopening crosswise of said direction varying in said direction ofdisplacement of said resonator.
 4. The resonator structure of claim 1,further including:a cavity defined by a housing made of an electricallyconductive material; said resonator and support plates being housed insaid cavity.
 5. The resonator structure of claim 2, further including:acavity defined by a housing made of an electrically conductive material;said resonator and support plates being housed in said cavity.
 6. Theresonator structure of claim 3, further including:a cavity defined by ahousing made of an electrically conductive material; said resonator andsupport plates being housed in said cavity.
 7. The resonator structureof claim 1, wherein:said resonator is made of a ceramic material.
 8. Theresonator structure of claim 2, wherein:said resonator is made of aceramic material.
 9. The resonator structure of claim 3, wherein:saidresonator is made of a ceramic material.
 10. The resonator structure ofclaim 1, wherein:said resonator is a cylindrical disk.
 11. The resonatorstructure of claim 2, wherein:said resonator is a cylindrical disk. 12.The resonator structure of claim 3, wherein:said resonator is acylindrical disk.